1. Field of the Invention
The present invention relates to a method of forming capacitors and, more particularly, to a method of forming high capacitance semiconductor capacitors with a single lithography step.
2. Description of the Related Art
A semiconductor capacitor is a well-known structure that typically includes two metal plates that are vertically separated by a dielectric layer. Semiconductor capacitors are commonly formed as part of the metal interconnect structure, which allows the capacitors to be formed without requiring any additional lithography steps.
For example, the lower capacitor plate can be formed at the same time that a first metal layer is etched to form a first layer of metal traces, while the upper capacitor plate can be formed at the same time that a second metal layer is etched to form a second layer of metal traces. In this case, the interlayer dielectric that electrically isolates the first layer of metal traces from the second layer of metal traces functions as the capacitor dielectric.
Although a capacitor which is formed as part of the metal interconnect structure does not require any additional lithography steps, and thus comes for free, the capacitance of the capacitor is limited by the available area and the requirements of the metal interconnect structure. In other words, the area that can be occupied by a capacitor, the vertical spacing between the first and second layers of metal traces, and the material used as the interlayer dielectric are defined by the requirements of the metal interconnect structure, not by the requirements of the capacitor.
Semiconductor capacitor structures, which include capacitors with multiple interdigitated plates and different dielectric materials, have higher capacitances than capacitors formed as part of the metal interconnect structure, but these semiconductor capacitor structures typically require a large number of lithography steps to form.
Lithography, in turn, is one of the most expensive steps in a semiconductor fabrication process. Thus, there is a need for a method of forming capacitors which have more substantially more capacitance than the capacitors formed as part of the metal interconnect structure and require fewer lithography steps than conventional high-value capacitors.